1. Field of the Invention
The present invention relates to measures to attain power supply at outage in a receiving side facility of a cable television broadcasting system using an optical fiber.
2. Description of Related Art
As known in Patent Document 1 to Patent Document 3, systems have recently been a focus of attention which broadcast announcement of various kinds of information through a cable television network in local communes and the like.
For example, as shown in FIG. 7, in a head end 10 of a network in a cable television broadcasting system using an optical fiber, an output mixer 170 mixes an audio information signal (70 to 90 MHz, for example) with a wavelength-multiplexed TV image signal (90 to 770 MHz, for example) to generate a broadband TV electric signal (70 to 770 MHz), and then an optical transmitter 180 converts the thus generated electric signal into an optical transmission signal in a predetermine wavelength band (1310-mn band or 1550-nm band, for example) and is sent it out to an optical transmission line 300 of a long distance formed of a single-mode optical fiber cable.
In each of subscriber's facilities 400, an optical receiver 500 receives the optical transmission signal transmitted through the transmission line 300 and coverts it into a TV electric signal (an RF signal) to output it. The thus output TV electric signal is input into a TV set 430 via a set-top box 420. Wherein, an AC power source environment 440 supplies electric power to the optical receiver 500 as well as to the set-top box 420 and the TV set 430.
Announcement broadcasting through such a network is performed in such a manner that the TV electric signal output from the optical receiver 500 is divided by a distributor 600 and an audio information signal is extracted from the thus divided TV electric signal by an announcement broadcasting terminal 460, such as an FM radio.
Patent Document 1: Japanese Unexamined Patent Application Publication 2002-368807 (page 5, FIG. 1)
Patent Document 2: Japanese Unexamined Patent Application Publication 2005-184700 (pages 5 to 7, FIG. 2)
Patent Document 3: Japanese Unexamined Patent Application Publication 2005-94310 (pages 2 to 3, FIG. 7 to FIG. 10)